Method and apparatus for tensioning strip

ABSTRACT

The disclosure of the present invention relates to a method and apparatus for controlling tension in a moving strip passing between two rolling mill stands. A piston cylinder assembly to which a strip-engaging roller is attached is employed to urge the strip away from a straight path of travel. On one side of the cylinder assembly roller a second roller is arranged to contact the strip and with which there is associated a load measuring device for measuring the tension in the passing strip. A signal representing the measured tension in the strip is compared with a signal representing a desired tension by a control that varies the operation of the piston cylinder assembly to reduce any difference between the two signals to a desired value, for example, a zero value.

UnitedStates Patent [191 Shurnaker Jan. 29, 1974 [54] METHOD AND APPARATUS FOR 3,485,427 12/1969 Busker 226/38 X TENSIONING STRIP 3,724,733 4/1973 Schaffer 226/25 Charles Storer Shumaker, Glenshaw, Pa.

Assignee: Wean United, Inc., Pittsburgh, Pa.

Filed: Nov. 1, 1972 Appl. No.: 302,687

Inventor:

Foreign Application Priority Data Jan. 21, 1972 Great Britain 2,934/72 References Cited UNITED STATES PATENTS 1 H1968 Tison et al. 226/39 X 5/1962 George et al. 226/25 UX 5/1970 Lewis, Jr. et al. 226/25 X Primary Examiner-Allen N. Knowles Attorney, Agent, or Firm-Henry C. Westin; Daniel Patch ABSTRACT The disclosure of the present invention relates to a method and apparatus for controlling tension in a moving strip passing between two rolling mill stands. A piston cylinder assembly to which a strip-engaging roller is attached is employed to urge the strip away from a straight path of travel. On one side of the cylinder assembly roller a second roller is arranged to contact the strip and with which there is associated a load measuring device for measuring the tension in the passing strip. A signal representing the measured tension in the strip is compared with a signal representing a desired tension by a control that varies the operation of the piston cylinder assembly to reduce any difference between the two signals to a desired value, for example, a zero value.

5 Claims, 2 Drawing Figures METHOD AND APPARATUS FOR TENSIONING STRIP Strip tension or tension measuring devices for rolling mills have taken, generally, two distinct forms. One,

particularly used in tandem cold mills, has been to employ a tight looper roller design, in which the strip is engaged by a more or less fixed tensiometer roller. In this design the tension in the strip was measured by the tensiometer roller and if found to be too high or low when compared with a desired tension value, the tension was adjusted by changing the speed of either one or both of the adjacent stands. The primary objection to this systern was found in the sluggishness or slowness of the response in effecting the desired change in the tension, in view of the fact that realization of the desired change in the tension was dependent on the time required to either slow down or speed up the large masses represented, in part, by the motorsdrives-spindlesand rolls of the mill.

The second form, sometimes referred to as a loose looper roller design, has been mainly used in the finishing stands of continuous hot strip mills and included a swingable looper roller that engaged and deflected the strip away from the steel line of the mill. The movement of the roller was usually accomplished by a piston cylinder assembly. The tension was controlled in this arrangement for the purpose noted above primarily by changing the pressure in the cylinder assembly, although it also sometimes included a speed adjustment of the adjacent mill stands. While the second form was much more rapid than the first tension control system, it has the serious disadvantage of not being as accurate as some mill operations required.

The present invention provides a method and apparatus for overcoming the disadvantages of the aforesaid former arrangements for use in both hot and cold rolling mills by providing a means for measuring the tension in the strip, a means for comparing the measured tension with a desired or preset tension value, and a means for varying effective force applied to the strip by a strip-engaging means to reduce any difference between the measured tension and the desired or preset tension to a desired value, for example, a zero value.

The present invention, more particularly, provides a very accurate means for measuring the tension in a strip as it passes between rolling mill stands in the form of a roller associated with a load cell, means for comparing the measured tension with a desired tension or preset tension value and should there be a difference producing a signal to effect a change in the pressure of a piston cylinder assembly that moves a looper roller, distinct from the measuring roller, into engagement with the strip to vary the strip tension to reduce the difference to a desired value.

A still further object of the present invention provides for the length of the strip that extends between two mill stands being controlled by a non-linear control device associated with the looper roller and which effects a change in the mill speed to keep the looper roller within a desired working range.

These objects, as well as other features and advantages of the present invention, will be better understood when the following description is read along with the accompanying drawings, of which:

In referring to FIG. 1 there is diagrammatically illustrated two adjacent mill stands 11 and 12 of a cold tandem rolling mill for reducing mild carbon steel strip while subject to interstand tension and moving in the direction of the arrow 13. The construction and operation of the mill stands follow well-known practice; in which FIG. 1 shows only one of the housing posts 14 and 15 of the mill stands and their respective working rolls 16 and 17 and backup rolls l8 and 19.

A strip tensioning and/or tension measuring apparatus 22, according to usual practice, is located between the adjacent housing posts 14 and 15 serving both to support the leading end of the strip when fed between the stands 11 and 12 and once rolling commences to control the tension in the strip imparted by the differential speeds of the stands. The apparatus illustrated in the drawings follows the teaching of the present inven tion which will now be described.

Associated with the mill stand 11, pivotally secured to the post 14 by a shaft 23, is a looper arm 24, to the outer end of which is rotatably carried a looper roller 25. Midway between the ends of the arms 24 and below the strip, the piston of a double-acting piston cylinder assembly 26 is secured to the arm; the cylinder itself being pivotally carried by the post 14. As shown in FIG. 1, the arm 24 and, more particularly, the looper roller 25, is rotated from a substantially horizontal position to a substantially vertical position in a clock-wise direction, in which the roller 25 is adapted to engage the underside surface of the strip.

' On the same side of the strip that the looper roller 25 is arranged, a second roller 29 is arranged to engage the strip. The roller 29 is rotatably mounted on the end of an arm 30 which is pivotally carried by a shaft 31 secured to the housing post 14. The arm 30 is provided with a flat surface 33 that engages the top surface of an electrical load cell 34 provided for accurately measuring the downward force imposed on the roller 29 by the strip. The load cell may take several well-known forms commonly employed in rolling mill applications. On the side of the strip opposite the rollers 25 and 29 a third freely rotatable roller 37 is arranged directly above the shafts 23 and 31 and adjustable relative to the strip by a vertical movable link 38.

Adjacent to the post 15 of the mill stand 12 is located a fourth roller 40 arranged normally above the strip and at an elevation slightly below the operative position of the roller 37. The roller 40 is mounted freely rotatably in a frame 41 which is adjustable vertically by virtue of a piston cylinder assembly 42. As noted in FIG. 1, the relationship and location of the rollers 25, 29, 37 and 40 are such that the strip is always held in positive contact with the tension measuring roller 29. Rollers 44 located between the working roll 17 of the mill stand 12 and the roller 25 are two of several provided to support the strip passing between the stands 11 and 12.

The piston cylinder assembly 26, the load cell 34 and the motor or motors for the stand 11 are inter-related by an electrical control in order to very accurately control the tension in the strip passing between the stands 11 and 12. The control includes a comparing amplifier 44 of a well-known type which receives an electrical signal over the line 45 representing a preset or desired tension in the strip as it passes between the stands 11 and 12. The preset or desired tension is compared in the amplifier 44 with a signal received over a line 46 from the load cell 34 representing the actual tension in the strip as determined from the force exerted by the strip against the roller 29. The amplifier 44 through a line 48 effects operation of a servo-valve 49 associated with the double-acting piston cylinder assembly 26. The extent and direction of operation of the piston cylinder assembly 26 is determined by a difference being ascertained between the two signals being sent to the amplifier 44. Should a difference exist between the desired and actual tension signals, the piston cylinder assembly 26 will be operated to reduce the difference to a desired value, such as, a zero value.

Also included in the tension control system is a nonlinear potentiometer 51 connected to the shaft 23 of the looper roller assembly. The potentiometer by a line 52 is connected to a speed regulator unit 53 which controls the speed of the motors 54 for working rolls 16 of the mill stand 11. FIG. 2 is a curve diagram of the nonlinear characteristic of the potentiometer 51 serving to better illustrate the working range of the looper arm 24 which is identified on the curve by the reference character 55, the midpoint of which is indicated in FIG. 1, as well as in FIG. 2.

The potentiometer is designed to cause a progressive increase or decrease in the speed of the motors 54 of the mill stand 11. The rate of change of speed, as shown in FIG. 2, immediately beyond the midpoint of the working range of the looper arm is, at first, very gradual; but at the outer ends of the curve the rate of change of speed becomes very rapid, both at the acceleration and deceleration directions.

In accordance with the provisions of the patent statutes, l have explained the principle and operation of my invention and have illustrated and described what I consider to represent the best embodiment thereof.

I claim:

1. In a method of controlling the tension in a strip passing between two stations comprising the steps of:

causing such strip to be engaged at two distinct points between said stations by a force exerting means and a tension measuring means,

establishing a tension in said strip between said two stations,

measuring the tension in said strip by said tension measuring means and producing a representative signal thereof,

producing a signal representative of a desired tension in said strip,

comparing the measured tension signal with the desired tension signal and producing a signal representing any difference between the two signals,

adjusting the tension in the strip by varying the force exerted by said force exerting means to increase or decrease the tension in the strip to reduce any difference between the measured tension signal and the desired tension signal to substantially zero, and

sensing the movement of said force exerting means and adjusting the speed of the strip passing by said force exerting means to maintain said force exerting means within a desired working range.

2. In a method of controlling the tension in a strip according to claim 1 wherein the adjustment of the speed of the strip passing by said force exerting means is characterized as non-linear and wherein the rate of change of the speed is gradual on adjacent sides of a selected working point in.the working range of said force exerting means and very rapid on points further away from said adjacent sides of said selected working point.

3. An apparatus for controlling the tension in a strip passing between two stations, comprising:

means for exerting a force on the strip so as to tension the strip as it passes between said stations,

means for measuring the tension in the strip,

means for producing a representative signal of the measured tension in the strip,

means for producing a signal representative of a desired tension in said strip,

means for comparing the measured tension signal with the desired tension signal and producing a signal representing any difference between the two signals,

means for adjusting the tension in the strip by varying the force exerted by said force exerting means to increase or decrease the tension in the strip to reduce any difference between the measured tension signal and the desired signal to substantially zero,

means for sensing the movement of said force exerting means, and

means for adjusting the speed of the strip passing by said force exerting means to maintain said force exerting means within a desired working range.

4. An apparatus for controlling the tension in the strip according to claim 3,

wherein said means for adjusting the speed of the strip passing by said force exerting means includes means for producing an electrical signal of a nonlinear characteristic and further characterized in that the rate of change of the speed is gradual on adjacent sides of a selected working point in the working range of said force exerting means and very rapid on points further away from said adjacent sides of said selected working point.

5. An apparatus for controlling the tension in a strip passing between two stations, comprising:

means for exerting a force on the strip so as to tension the strip as it passes between said stations,

means for measuring the tension in the strip,

means for producing a representative signal of the measured tension in the strip,

means for adjusting the tension in the strip by varying the force exerted by said force exerting means until the measured tension in the strip equals a desired tension, and

wherein a first roller is connected to said force exerting means and engageable with said strip,

a second roller associated with said means for measuring the tension in the strip arranged to engage the strip,

a third roller arranged between said first and second rollers adapted to engage the strip in a manner to cause the strip to deflect between said first and second rollers,

a fourth roller arranged adjacent the first roller on the side furthest away from said third roller in a manner to engage the strip, and

said first and second rollers being located on the side of the strip opposite the third and fourth rollers. 

1. In a method of controlling the tension in a strip passing between two stations comprising the steps of: causing such strip to be engaged at two distinct points between said stations by a force exerting means and a tension measuring means, establishing a tension in said strip between said two stations, measuring the tension in said strip by said tension measuring means and producing a representative signal thereof, producing a signal representative of a desired tension in said strip, comparing the measured tension signal with the desired tension signal and producing a signal representing any difference between the two signals, adjusting the tension in the strip by varying the force exerted by said force exerting means to increase or decrease the tension in the strip to reduce any difference between the measured tension signal and the desired tension signal to substantially zero, and sensing the movement of said force exerting means and adjusting the speed of the strip passing by said force exerting means to maintain said force exerting means within a desired working range.
 2. In a method of controlling the tension in a strip according to claim 1 wherein the adjustment of the speed of the strip passing by said force exerting means is characterized as non-linear and wherein the rate of change of the speed is gradual on adjacent sides of a selected working point in the working range of said force exerting means and very rapid on points further away from said adjacent sides of said selected working point.
 3. An apparatus for controlling the tension in a strip passing between two stations, cOmprising: means for exerting a force on the strip so as to tension the strip as it passes between said stations, means for measuring the tension in the strip, means for producing a representative signal of the measured tension in the strip, means for producing a signal representative of a desired tension in said strip, means for comparing the measured tension signal with the desired tension signal and producing a signal representing any difference between the two signals, means for adjusting the tension in the strip by varying the force exerted by said force exerting means to increase or decrease the tension in the strip to reduce any difference between the measured tension signal and the desired signal to substantially zero, means for sensing the movement of said force exerting means, and means for adjusting the speed of the strip passing by said force exerting means to maintain said force exerting means within a desired working range.
 4. An apparatus for controlling the tension in the strip according to claim 3, wherein said means for adjusting the speed of the strip passing by said force exerting means includes means for producing an electrical signal of a non-linear characteristic and further characterized in that the rate of change of the speed is gradual on adjacent sides of a selected working point in the working range of said force exerting means and very rapid on points further away from said adjacent sides of said selected working point.
 5. An apparatus for controlling the tension in a strip passing between two stations, comprising: means for exerting a force on the strip so as to tension the strip as it passes between said stations, means for measuring the tension in the strip, means for producing a representative signal of the measured tension in the strip, means for adjusting the tension in the strip by varying the force exerted by said force exerting means until the measured tension in the strip equals a desired tension, and wherein a first roller is connected to said force exerting means and engageable with said strip, a second roller associated with said means for measuring the tension in the strip arranged to engage the strip, a third roller arranged between said first and second rollers adapted to engage the strip in a manner to cause the strip to deflect between said first and second rollers, a fourth roller arranged adjacent the first roller on the side furthest away from said third roller in a manner to engage the strip, and said first and second rollers being located on the side of the strip opposite the third and fourth rollers. 